One of the nation's most outspoken anti-abortion rights groups is putting an unwelcome spotlight on Mitt Romney's anti-abortion credentials.

The former Massachusetts governor's position on the issue, which has evolved over time, became a distraction during his 2008 run for president. Earlier this week, he stated on national television that he is "firmly pro-life."

But the Susan B. Anthony List reported Friday afternoon that Romney was the only top-tier 2012 presidential candidate to refuse to sign its "Pro-Life Leadership Presidential Pledge."

"The fact of the matter is that thus far he has refused to sign," former Rep. Marilyn Musgrave, a SBA List project director, told Roll Call in a telephone interview from New Orleans, where she was poised to highlight news of the pledge at the Republican Leadership Conference.

She warned of political consequences for Romney and others who refused to sign the pledge.

"When you look at the primary voter, they are overwhelmingly pro-life," Musgrave said. "We believe that it is politically advantageous, not to mention the right thing to do, to sign our pledge."

The Romney camp acknowledges discussing the issue with the pro-life group, but ultimately decided the pledge was overly broad. Among other concerns cited by the Romney cited, the pledge calls for legislation to strip taxpayer funding from Planned Parenthood and "all other contractors and recipients of federal funds with affiliates that perform or fund abortions."

That could include a large number of hospitals.

"Governor Romney pledged in the last campaign that he would be a pro-life president and of course he pledges it today," Romney spokeswoman Andrea Saul said. "However, this well intentioned effort has some potentially unforeseen consequences and he does not feel he could in good conscience sign it."

No doubt the issue could raise questions for those who did and did not sign. The Planned Parenthood debate, for example, while popular among some Republican voters, threatens to alienate women next fall.

Signers in the GOP field include former Minnesota Gov. Tim Pawlenty, Rep. Michele Bachmann (Minn.), former Sen. Rick Santorum (Pa.), former Speaker Newt Gingrich (Ga.) and Rep. Ron Paul (Texas). The offer to sign the pledge was extended to anyone who had formed an exploratory committee, according to Musgrave. (Neither former Utah Gov. Jon Huntsman nor Texas Gov. Rick Perry, who have yet to form any committee but may enter the race, were asked to sign.).

Romney may be the early frontrunner in the 2012 Republican primary, but he has struggled to win over cultural conservatives in some cases. Just two other candidates refused to sign the pledge: former Godfather's Pizza CEO Herman Cain and former New Mexico Gov. Gary Johnson.

That's not exactly company the Romney camp would like to join.

In a subsequent statement distributed to reporters across the country, Musgrave took a not-so-subtle shot at Romney, while declining to use his name.

"We applaud those candidates who did sign the pledge for vowing to support and advance the protection of life at all stages if elected to the White House," she said. "Their signatures demonstrate that mere lip-service to protecting women and the unborn is not enough — it must be backed up by concrete action."

In addition to the taxpayer funding language, the pledge states that if elected, the candidate would support only Supreme Court nominees who are committed to "applying the original meaning of the Constitution" and "would select pro-life appointees for relevant cabinet and executive branch positions."

Romney's decision would seem to play better with general election voters. But among the more socially-conservative Republicans who vote in primaries, his abortion position could be a problem.

"I know the economy is the top issue, but the life issue can make the race," Musgrave said. "It's the pro-life people who show up."

Romney, meanwhile, hopes to patch things up with the SBA List, despite his refusal to sign.

"Governor Romney has been a strong supporter of the SBA List in the past and he looks forward to continue working with them to promote a culture of life," Saul said.